a. Field of the Invention
The instant invention generally relates to devices and methods for treating electrophysiological diseases of the heart. In particular, the instant invention relates to devices and methods for ablation for the treatment of atrial fibrillation.
b. Background Art
It is well known that atrial fibrillation results from disorganized electrical activity in the heart muscle (the myocardium). The surgical maze procedure has been developed for treating atrial fibrillation, and involves the creation of a series of surgical incisions through the atrial myocardium in a preselected pattern so as to create conductive corridors of viable tissue bounded by scar tissue.
As an alternative to the surgical incisions of the maze procedure, transmural ablations of the heart may be used. Such ablations may be performed either from within the chambers of the heart (endocardial ablation), using endovascular devices (e.g., catheters) introduced through arteries or veins, or from outside the heart (epicardial ablation) using devices introduced into the patient's chest via thoracic incisions (e.g., thoracotomies). Various ablation techniques may be used, including, but not limited to, cryogenic ablation, radio frequency (RF) ablation, laser ablation, ultrasonic ablation, and microwave ablation. The ablation devices are used to create elongated transmural lesions—that is, extended blocking lesions passing through a sufficient thickness of the myocardium to block electrical conduction—forming the boundaries of the conductive corridors in the atrial myocardium. Perhaps most advantageous about the use of transmural ablation rather than surgical incision is the ability to perform ablation procedures without first establishing cardiopulmonary bypass (CPB).
A transmural lesion need not, however, extend all the way to the surface of the tissue being treated. This is particularly true for ventricular burns and ventricular rhythm disorders. Often, there are structures, such as coronary arteries, near the surface of the ventricular tissue, that are to be protected from thermal damage and/or thermal necrosis when creating transmural lesions in deeper tissue. With certain ablation techniques, such as RF ablation and cryogenic ablation, it is difficult to create effective sub-surface lesions without also causing thermal damage and/or thermal necrosis in this more superficial tissue. Indeed, many ablation techniques cannot effectively be used to deliver sufficient ablative energy to create an effective lesion in deeper tissue without also delivering sufficient energy to thermally damage more superficial tissue.